Chapter 6 Energy, Enzymes, and Metabolism

Biology 101

Tri-County Technical College

Pendleton, SC

Metabolism and more…

Metabolism defined as sum of all chemical reactions in a cell

Anabolism is part of metabolism concerned with building up complexity in cell Requires energy to accomplish

Catabolism is part of metabolism concerned with breaking down complex substances into simpler ones and releasing energy in process

Reactions are often linked (coupled)

Thermodynamics

Energy defined as ability to do workWork defined as movement of mass through spaceKinetic versus potential energyIn biochemistry, energy represents capacity for changeFirst Law: energy (matter) cannot be created nor destroyed Can be converted from one form to another

Thermodynamics, cont.

Chemical to light; mechanical to electrical; potential to kinetic; and vise versaLaw applies to the universe or any closed systemOpen system merely one part of larger closed systemLaw states that in any interconversion, the total energy before and after the conversion is the SAME

Thermodynamics III

Second law states that “in every energy conversion, some of the energy becomes unavailable to do work” Some lost to entropy (disorder)/some as heat

Total energy called enthalpy (H)Usable energy (doing work) is called free energy (G)Unusable energy called entropy (S) which is multiplied by absolute temperature

Thermodynamics IV

H = G + TS Can be rewritten to G = H – TSEnergy changes measured in calories (cal) or joules (j)Change in value represented by Δ (delta) and can be negative or positiveIf ΔG is negative, free energy released; if positive, free energy consumed Endergonic versus exergonic reactions

Exo versus Ender Visual

Energy Coin of the Realm

Adenosine triphosphate (ATP)

Can be hydrolyzed and can donate a phosphate group to many different compounds

ADP-ATP cycle classic example of energy coupling and biochemical reaction Couples endergonic and exergonic reactions

Time for an Estesism…Hot damn!!!

ATP Visual

ADP-ATP Cycle Visual

…but how does it work

Phosphate groups are negatively charged

Lots of free energy required to overcome tendencies of phosphates to repel each other

Energy invested to make ADP from AMP and ATP from ADP

When phosphate removed, energy used to put it there released and used to do work

Active cells requires millions of ATPs per second to drive its machinery

Energy Coupling Visual

Here and there..mostly there

Catalyst is any substance that speeds up chemical reaction w/o itself being used upMost biological catalysts are proteins called enzymes Certain RNA molecules (ribozymes) TOO

**Reactions would proceed eventually given infinityNot fast enough or often enough to sustain life

Enzymes, cont.

ApoenzymeHoloenzymeCoenzymes and cofactorsFor reaction to proceed, energy barrier must be overcome**Exergonic reactions proceed ONLY after they are pushed over energy barrier by small amount of added energyNeeded energy called activation energy (EA)

Enzymes III

EA changes reactants into unstable molecular forms called transition-state species

Could lower EA by >ing temperatureSucrose and bunsen burner..care for a light?

Enzymes work by lowering EA so reaction can proceed at temperature favorable to lifeSome can catalyze 400 million reactions/sec Liver enzyme catalyse

Activation Energy Visual

Enzymes and Substrates

In enzyme-catalyzed reactions, reactants are called substrates

Substrates bind to a particular site on enzyme called the active site

Specificity of enzyme results from exact 3-dimensional shape and structure of enzyme

Reason enzyme recognizes its substrate is because it “fits”

Most enzyme names end in “ase”

Enzymes, cont.

Enzyme-substrate complexreaction

Enzymes lower EA by one/more processes Orient substrates Add charges to substrates Induce strain in the substrates

Competitive and noncompetitive inhibition

Two models of enzyme specificity “Lock and key” and “induced fit”

Induced fit most widely accepted model

Enzyme-Substrate Visual

Induced Fit Visual

Factors Affecting Rate

No enzyme present, reaction rate would be directly proportional to [ ] of substrate Higher [ ], the more collisions=more reactions

Addition of enzyme speeds up reaction and changes plot of reaction

Rate >es as substrate >es but then levels off

Enzyme has become saturated (working as fast as it can)

Factors, cont.

Turnover number = number of molecules converted to product in one secondIf enzyme saturated, adding more substrate will NOT > reaction rate any furtherMost enzymes have optimal pH rangeTemperature affects enzyme activity Warming >es rate but only to a point; becomes too

warm, enzyme begins to denature (nonfunctional)

Isozymes (enzymes that catalyze same reaction but have different optimal temps) made by many organisms

And finally, brethren…

Let’s briefly discuss negative feedback model